In the new play “Open House,” which Tallgrass Theatre opened this past weekend in West Des Moines, one of the owners of the house keeps hearing strange noises — a creaky floorboard, a gurgling in the basement.

Although it’s possible the old farmhouse is just settling, she doubts it.

“It’s 120 years old,” she says. “It’s settled.”

But don’t believe her. Nothing is quite as it seems in this quietly unsettling story by Craig Owens, who teaches play­writing at Drake University and whose script won Tallgrass’ seventh annual Iowa Playwrights Workshop competition. His original draft went through a series of critiques and revisions over the last few months — with feedback from actors, test audiences and director Stephanie Clemens — and the final product is a well-crafted story that, like its title subject, has mysterious cracks in its foundation.

To its credit, I’m not exactly sure what happened in the end.

So let’s start with the basics. The woman who hears the noises is Mary (Erika Hakmiller), who moved to the house in northern Illinois with her better half, John (Jason Rainwater), when he landed a professorship at the local college. He teaches in the field of literary theory known as poetics, which gives both him and her license to speak in academese. (Both actors pull it off well, in addition to convincing us they’re at least 20 years older than they really are.)

They first appear in their bathrobes, hours before sunrise on the day they’ve agreed to open their house for a tour of historic homes. They’re a little stressed out by the ordeal, and they bicker. But they’re not too upset to slow dance around the dining room when John puts on a record to ease Mary’s mind.

The real trouble begins with the unexpected arrival of their wiry son Jesse (Jordan Jepson), back with some awkward news after his first months at a college out of town.

“There’s this girl ... ,” he mumbles, fessing up that — oops — he got her pregnant and — oops, again — she happens to be passed out in his car at that very moment.

His parents are less than pleased. They haul her inside and stretch her out under the dining room table, where she eventually wakes up in a state of unusual composure. She introduces herself as Emily (the excellent Jessica Vaught) and coolly proceeds to make herself at home, asking for breakfast and a shower.

And here’s where things get weird. The natural back-and-forth dialogue in the first act warps into longer monologues in the second, when the characters behave in ways that don’t make sense — or at least, don’t make sense with what they led us to expect. Professor John and Emily are disturbingly flirtatious, and Mary switches into mama-bear mode, either to protect her dimwit son or for reasons of her own. You start to wonder if you missed clues they dropped along the way.

Set designer Ryan Patrick Hawkins furnished the stage with a few elegant details, and sound designer Ryan Schmitz smoothed the transitions with baroque music, lending a bit of polish to the domestic mess. The windy sounds that seemed to howl outside the house were either good recordings or the real deal, whipping across the theater’s roof.